The interconnections of the neural elements of the Necturus retina, particularly in the inner plexiform layer, will be investigated electro-physiologically using a combination of quantitative, analytic, and pharmacological approaches. The linearity of spatial summation within the receptive fields of bipolar cells and amacrine cells will be tested, and the results compared with the spatial summation properties of the several types of ganglion cells. The nature and sequence of the non-linearities in the retinal networks preceding the various types of bipolar cells, amacrine cells, and ganglion cells will be determined. This will be done by analysing data from two-spot spatial summation experiments using the methods developed by Levine and Abramov (Vision Res. 15, 777-789). Ganglion cell responses will be recorded extra-cellularly; bipolar and amacrine cell responses, intracellularly. The effects of agonists and antagonists of putative retinal neurotransmitters (GABA, glycine, catecholamines, and acetylcholine) will also be examined. The effects of the various drugs on the receptive field properties of bipolar, amacrine, and the various types of ganglion cells will be determined. An effort will be made to determine whether each effective drug acts directly on the affected cell or at some site earlier in the retina. The changes the various effective drugs produce in the networks preceding the bipolar, amacrine, and ganglion cells will also be determined using the Levine-Abramov analysis. Transmitter agonsits should enhance, and antagonists should eliminate, the network features due to individual transmitters. Comparisons of the spatial summation properties of and experimentally determined networks preceding the various types of ganglion cells with those of bipolar and amacrine cells, and the pattern of effects of the various drugs on all three cell types, will allow inferences to be made concerning the nature and extent of bipolar cell and/or amacrine cell input to the various types of ganglion cells.